Gene regulation and biotechnology
Every cell has the same genes, but each uses only some of them. Controlling which genes are on is central to development, health, and disease.
Why regulate genes?
A liver cell and a nerve cell contain the same DNA but make different proteins. Gene regulation turns genes on and off as needed, saving energy and letting cells specialise. Errors in regulation contribute to cancer and developmental disorders.
The lac operon
In bacteria, related genes are often grouped in an operon controlled by one switch. E. coli's lac operon makes enzymes to digest lactose. When lactose is absent, a repressor protein blocks transcription; when lactose is present, it binds the repressor and releases it, switching the genes on.
Eukaryotic regulation
Eukaryotes control genes at many levels. Transcription factors bind DNA near genes to boost or block transcription. Tightly packed DNA is harder to read, so chemical tags on DNA and histones (epigenetic marks) can silence genes. Cells also control mRNA processing, lifespan, and translation.
Epigenetics
Epigenetic marks, such as methyl groups added to DNA, change gene activity without changing the sequence. Some are influenced by environment, such as diet or stress, and a few may pass to offspring. Identical twins accumulate different epigenetic marks as they age.
Development and stem cells
During development, a fertilised egg divides and cells switch on different gene sets to become specialised. Hox genes control body plan, deciding where heads, limbs, and segments form. Stem cells can still become many cell types; embryonic stem cells can become any type, while adult stem cells are more limited.
Cancer as gene regulation failure
Cancer arises when mutations disrupt genes controlling the cell cycle. Oncogenes are mutated genes that push cells to divide, like a stuck accelerator. Tumour suppressor genes, such as p53, normally stop division or trigger cell death; when broken, the brakes fail. Most cancers need several mutations.
Biotechnology tools
Restriction enzymes cut DNA at specific sequences; DNA ligase pastes pieces together. Gel electrophoresis separates DNA fragments by size, used in DNA fingerprinting. Plasmids carry genes into bacteria to make products like insulin. CRISPR can edit genes precisely.
Applications and ethics
Biotechnology produces medicines, diagnoses genetic disease, solves crimes through DNA profiling, and creates crops with improved traits. Gene therapy treats some inherited diseases by adding working genes. Debates continue over privacy of genetic data, genetically modified food, and editing human embryos.
Key takeaways
Gene regulation lets cells with identical DNA specialise. Bacterial operons like lac are switched by repressors. Eukaryotes use transcription factors, epigenetic marks, and later controls. Hox genes shape body plans; stem cells can become many types. Cancer involves overactive oncogenes and broken tumour suppressors. Biotechnology tools cut, paste, separate, and edit DNA.
Flashcard
Turning genes on and off
Check your understanding
In the lac operon, what happens when lactose is present?